[PATCH v2] rtc: fix overflow and incorrect calculation in rtc_time64_to_tm

[Sasha Levin <sasha.levin@oracle.com>]

At some point after humans go extinct and robots cotrol the world, dividing
he time64_t by 86400 to extract the days will overflow a 32bit integer,
leading to incorrect conversion into rtc_time in rtc_time64_to_tm().

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
---
 drivers/rtc/rtc-lib.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/rtc/rtc-lib.c b/drivers/rtc/rtc-lib.c
index e6bfb9c..cafae93 100644
--- a/drivers/rtc/rtc-lib.c
+++ b/drivers/rtc/rtc-lib.c
@@ -53,12 +53,11 @@ EXPORT_SYMBOL(rtc_year_days);
 void rtc_time64_to_tm(time64_t time, struct rtc_time *tm)
 {
 	unsigned int month, year;
-	unsigned long secs;
-	int days;
+	int secs;
+	time64_t days;
 
 	/* time must be positive */
-	days = div_s64(time, 86400);
-	secs = time - (unsigned int) days * 86400;
+	days = div_s64_rem(time, 86400, &secs);
 
 	/* day of the week, 1970-01-01 was a Thursday */
 	tm->tm_wday = (days + 4) % 7;
-- 
1.7.10.4